For a variety of reasons, plant species may be intentionally bred. For example, in some applications plant species are intentionally bred to form hybrid plant species. In some applications, hybrid plants are bred to exhibit various desirable traits. Such traits may include, for example, resistance to heat and drought, resistance to disease and insect damage, improved yield characteristics, and improved agronomic quality. In general, plants may be capable of self-pollination, cross-pollination, or both. Self-pollination describes pollination using pollen from one flower that is transferred to the same or another flower of the same plant. Cross-pollination describes pollination using pollen delivered from a flower of a different plant from a different family or line.
Plants that have been self-pollinated and selected for many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. A cross between two different homozygous lines produces a uniform population of hybrid plants that may be heterozygous for many gene loci. A cross of two plants each heterozygous at a number of gene loci will produce a population of heterogeneous plants that differ genetically and will not be uniform.
Maize (Zea mays L.), often referred to as corn in the United States, can be bred by both self-pollination and cross-pollination techniques. Maize has separate male and female flowers on the same plant. The male flowers are located on the tassel and the female flowers are located on the ear. Natural pollination occurs in maize when wind blows pollen from the tassels to the silks that protrude from the tops of the ears.
The development of a hybrid maize variety in a maize seed production program involves three steps: (1) the selection of plants from various germplasm pools for initial breeding crosses; (2) self-pollination of the selected plants from the breeding crosses for several generations to produce a series of inbred lines, which, individually breed true and are highly uniform; and (3) crossing a selected inbred line with an unrelated inbred line to produce the hybrid progeny. After a sufficient amount of inbreeding successive filial generations will merely serve to increase seed of the developed inbred. Preferably, an inbred line should comprise homozygous alleles at about 95% or more of its loci.
During the maize inbreeding process, vigor of the lines decreases. Vigor is restored when two different inbred lines are crossed to produce the hybrid progeny. An important consequence of the homozygosity and homogeneity of the inbred lines is that the hybrid between a defined pair of inbreds may be reproduced indefinitely as long as the homogeneity of the inbred parents is maintained. Once the inbreds that create a superior hybrid have been identified, a continual supply of the hybrid seed can be produced using these inbred parents and the hybrid corn plants can then be generated from this hybrid seed supply.
Achieving synchronization between male parent flowering and female parent flowering (sometimes called “niche”) is often a desirable step in maximizing successful cross-pollination of plants that are planted in the same or neighboring fields. Several techniques are known in the art to improve this synchronization. For example, one technique involves planting several rows of female parent plants and one row of a male parent plant adjacent the several rows of female parent plants. At some later time, another row of male parent plants is planted adjacent the first row of male parent plants. This is sometimes referred to as “split male delay planting” and results in an extended pollination period due to the delayed pollination production from the second row of male plants. Another technique involves planting male and female parent plants and then cutting a portion of the leaf tissue of a row of emerging male parent plants in order to shock the plants and delay their development and production of pollen. This technique also results in an extended pollination period due to the delayed pollination production from the male plants that were cut.
The above techniques, however, have certain disadvantages. For example, prior art delay planting often produces excess competition between the first and second rows of flowering male plants, resulting in less than ideal pollination of the female plants. Additionally, depending on the orientation of the plants in a particular field, the first row of male plants planted using prior art delay planting may shade the second row of male plants, which can suppress or impede proper development of the second row of male plants and thus affect the level and timing of pollination from the male plants. If cutting is used, the cut plants may have reduced stature and pollen yield, and may also be more susceptible to some diseases. In addition, pathogens causing viral or bacterial infections may be transmitted from a diseased plant to a healthy plant via the cutting mechanism or device.
As a result of the above, there is a need in the art for an improved method for planting seeds to extend the duration of pollen availability. In various embodiments, the method should provide an efficient solution for facilitating cross-pollination of female plants. For example, the method should provide efficient use of male plants so as to maximize planting space and should also provide accurate placement of male plants with respect to the female plants.